Optical element driving devices such as a galvanometer mirror using a mirror for diffracting a luminous flux are used in optical devices such as an information read-write device for reading and/or writing information to and/or from an information medium such as an optical disk drive, a write-once-read-many optical disk drive, a phase-change optical disk drive, a CD-ROM, a DVD, an optical card or the like, and also used in other optical devices such as an optical scanner or the like.
As an optical element driving device, an exemplary galvanometer mirror 61 shown in FIGS. 16A and 16B is disclosed in Japanese Unexamined Patent Application Publication No. 5-12686. Note that FIG. 16A illustrates a sectional structure of the galvanometer mirror 61 and FIG. 16B illustrates a partial plan view of the galvanometer mirror 61.
The galvanometer mirror 61 has a round reflecting mirror 65 disposed therein, and a plurality of coils 66a to 66e wound in a rectangular shape that is arranged on the rear surface of the reflecting mirror 65, each in a symmetrical manner with respect to the center of the reflecting mirror 65, and that is fixed to the side surface of the reflecting mirror 65 by bending two short sides of each of the coils 66a to 66e. The reflecting mirror 65 is fixed on the upper surface of a mirror support 67 and is rotatably supported in substantially any given direction by attaching the mirror support 67 to a tubular housing 70 via a hinge 68 and a base 69, wherein the hinge 68 is integrally formed in the middle of the rear surface of the mirror support 67.
Also, the housing 70 has a ring-shaped back yoke 71 disposed thereon so as to face the side surface of the reflecting mirror 65 and has a multipolar magnet 72 on the inner surface of the back yoke 71 disposed thereon such that the poles of the multipolar magnets face the corresponding bent parts of the coils 66a to 66e, wherein the bent parts are fixed to the side surface of the reflecting mirror 65. This arrangement allows the reflecting mirror 65 to rotate around a rotation axis lying in a direction orthogonal to the coil in question by applying electric current to the desired coil so as to generate forces at the two short sides thereof in mutually opposite directions. For example, electric current applied to the coil 66c flows in the two short sides of the coil 66c in mutually opposite X-directions, thereby allowing forces generated by an electromagnetic interaction with the magnetic fields of the multipolar magnet 72 to act on the two short sides in mutually opposite directions perpendicular to the plane of the drawing. In other words, upward and downward forces act on the respective short sides of the coil 66c in the mutually opposite directions perpendicular to the plane of the drawing. As a result, the reflecting mirror 65 rotates around X-axis. Also, concurrently applying electric current to adjacent two coils with desired current ratios allows the reflecting mirror 65 to rotate around any given rotation axis.
A plurality of coils on which a plurality of forces acts is arranged at one side relative to the hinge 68, which is a supporting member and acts as a tilting center, in the direction perpendicular to the reflection surface of the reflecting mirror 65. Although the hinge 68, the mirror support 67, and the base 69 are integrally formed, the hinge 68 acts as the supporting member for tiltably supporting the mirror by changing its shape. The mirror support 67 and the base 69 do not change their shapes when tilting the mirror and have a function as a structural member. The hinge 68 changes its shape when tilting the mirror and acts as a tilting center.
The magnetic fields of the magnet 72 generates upward and downward forces at driving points D indicated in FIG. 16A on the short sides of a coil in the opposite directions parallel to the plane of the drawing, leading to a torque generated around the hinge 68 on the moving body including the mirror 65, thereby tilting the moving body around the hinge 68. The center of torque of the forces generated at the driving points D on both sides lies at Da.
In the galvanometer mirror 61, the mirror 65 is configured so as to be driven and supported in multi-directions such that parts of the coils 66a to 66e for tilting the mirror 65 in multi-directions are disposed so as to be sandwiched between the mirror 65 and the supporting member for supporting the mirror 65, effective sides of the coils generating forces are bent and disposed on the side surface of the mirror 65, the magnet 72 is disposed outside the outer periphery of the coils, and the linear hinge-like support, which has a circular cross-section, of the supporting member is disposed on the rear surface of the mirror 65.
Incidentally, in the known example shown in FIGS. 16A and 16B, the mirror 65, the driving coils 66a to 66e, and the magnet 72 are disposed at one side of the hinge 68 at which the rotation axis of the tilting mirror 65 lies, and which serves as the tilting center and the supporting member.
This arrangement causes a difficulty in that the center of torque Da generated at the driving points D of the coils 66a to 66e lies at the hinge 68. Also, the center of gravity G of the moving body of the known example lies away from the hinge 68 since the mirror 65 and the coils 66a to 66e are disposed at one side of the hinge 68, causing a difficulty in that the supporting member lies at the center of gravity, giving rise to a problem in which resonance takes place when the mirror 65 is driven for tilting, accordingly causing the driving characteristics to deteriorate.
The present invention is made in view of the above problem. An object of the present invention is to provide a galvanometer mirror that can be set such that the center of torque acting on the moving body lies near the center of gravity of the moving body or near the center of the movable support when the mirror is driven for tilting and that has excellent driving characteristics.